In automated or automatic manual transmissions, these electric motors are usually attached to the outside of the transmission housing. A transmission of this type is known from DE 103 44 106 A1, for example. That particular publication describes an electric motor that is screwed onto the outside of the transmission housing. The electric motor drives a gear that engages a shifting shaft through an opening in the wall of the transmission housing. In this type of arrangement, the engaging surface must naturally be painstakingly sealed. The sealing site is also the mechanical interface between the electric motor and the transmission housing, since the motor is attached to the transmission housing at this location by screw connections. When interfaces have multiple functions as described above, it is technically very difficult to ensure that all functions perform satisfactorily. Furthermore, it must be taken into consideration that the electric motor, attached to the outside of the transmission housing, constitutes a vibratable component that can be damaged by excessive resonance resulting from vibrational excitation generated by the transmission. Because of its exposed location, the electric motor is naturally subjected to strong temperature fluctuations. Through its own heat and the additional heat from the transmission, it can reach a temperature that considerably exceeds the temperature of the surrounding medium such as spray water, for example. Quenching with the surrounding medium causes pressure differences to appear at the sealing surface, which in turn increase the stress placed on the interface seal.
DE 103 07 017 A 1 also discloses an electromechanically actuated transfer case in which an electric motor actuates a clutch device, via a drive converter device.
In that system, a first output shaft is directly connected to a drive shaft. A second output shaft can be connected to the drive, via a clutch device.
The clutch device can be actuated by the electric motor, while arranged between the clutch device and the electric motor is a device via which a rotational movement of the electric motor is transformed into a translatory actuation movement for controlling the clutch device.
The electric motor, in this example, is equipped with a motor housing and is installed in the transmission housing completely preassembled. The separate motor housing of the electric motor is nonrotatably attached to the transmission housing. The installation of a separate motor housing also involves a mechanical interface that is technically difficult to realize. This results in a weak spot that can make the product more prone to defects.